Is anyone using an automotive LED trailer light as a rear light?

I've been thinking about picking up one of these from Amazon:

I have an HID light laying around at home that's not being used anymore, so I've been thinking about taking the 14.4V battery from that and hooking it up to one of these LED trailer lights, and using that on the back of my rack. I could hook it up so that it lights up the regular light plus the brake light, should be pretty bright, and since it's about six inches across, I was thinking it would be easier to gauge the distance to my bike from a car driver's perspective. I'd have to be mindful about not letting the battery voltage get too low, no built-in cutoff on that (older) battery pack. Anyone doing something like this?

I have one, but stopped using it. I don't really remember why, it's been a couple of years. Mine came from Lowes, and was powered by AA batteries. People asked me where I got it, so I took that as an endorsement of its visibility.

If it's a DOT approved brake light, it will be plenty bright. I wonder what the current draw is. Doing something like this isn't something I'm contemplating, but if I were, I'd build a low voltage cutoff and flasher circuit for it.

i use a cygolite 2 watt rechargeable tail lamp when i ride in traffic.
they seem to be much cheaper this year on ebay. http://www.ebay.com/itm/Cygolite-Hot...item2a27c8af2e
actually i use 3 of them, 1 steady non flasher and 2 flasher pinned to my hips.
i get comments from other bikers that they see my lights from almost 1 mile away during daylight hours.

I have an HID light laying around at home that's not being used anymore, so I've been thinking about taking the 14.4V battery from that and hooking it up to one of these LED trailer lights, and using that on the back of my rack. I could hook it up so that it lights up the regular light plus the brake light, should be pretty bright, and since it's about six inches across, I was thinking it would be easier to gauge the distance to my bike from a car driver's perspective. I'd have to be mindful about not letting the battery voltage get too low, no built-in cutoff on that (older) battery pack. Anyone doing something like this?

Not quite like that, but I am using a 12V system so here's a suggestion: The voltage input range that your light engine uses will determine how your battery is impacted. My engine requires a minimum of 9V which lets me use a 3S1P without protection. As soon as the output drops below 9V (3x3) the system shuts down.

So check out the specs on that tail-light and decide your electrical requirements in consequence. One thing I WOULD definately suggest is using 12 AWG silicone shielded, stranded copper wire everywhere. That'll give you minimum issues in cold weather and high vibration environments.

I use the 12V version from Optronics, it's great. STL78, it runs about 3 watts (running the brake light circuit instead of the taillight circuit) and also is somewhat diffuse due to the number of diodes and their mounting pattern. About $20 as I remember at your local auto parts store (also available online)

crappy cellphone pic below, can't tell you the exposure or details, but that's what it looks like in the dark, I don't have to turn and look to see if it's on in the dark, I can see the road reflection of the red beam in my rearview mirror, it's bright.

I used a similar 12V trailer light as part of my homebrew lighting system some years ago. I wired mine into an integrated 14.4V system with a digital controller that automatically overvolted my 20W halogen headlights and drove my tail light and an amber strobe in back.

That system was insanely bright and ate juice like crazy. On full blast it would generate so much heat that you could hear rain drops sizzle on the headlights. It also drained a 5AH battery in just under an hour in overdrive.

I abandoned that system because I got tired of carrying a heavy battery with wires run all over my bike. I like the new crop of battery powered tail lights that are available now.

That said: The light was dependable and bright. But it was bulky and inefficient compared to the nicer bicycle specific lights on the market.

Last edited by Hydrated; 01-08-13 at 01:35 PM.
Reason: To actually answer the question.

It is the mark of an educated mind to be able to entertain a thought without accepting it.-Aristotle

My brightest tail light is a Cygolite ExpiliOn 450 that I converted from a head light to a tail light by putting 3 layers of red tail light tape used to fix broken tail lights. This gave me probably the brightest tail light available on the market with 450 lumens and I did it far cheaper then some other brands boasting 400 lumen tail lights, and my battery is self contained.

I tried one of those from Lowes that runs on AA batteries (intended as a temporary light - it had a magnetic and one or two other attachment mechanisms, intended to be slapped onto the back of weird/long/oversize loads). It was bright but not as bright as the Dinotte or the MagicShine taillight so I returned it. I did a review with photos but that was like 6 years ago and I can't find it.

My brightest tail light is a Cygolite ExpiliOn 450 that I converted from a head light to a tail light by putting 3 layers of red tail light tape used to fix broken tail lights. This gave me probably the brightest tail light available on the market with 450 lumens and I did it far cheaper then some other brands boasting 400 lumen tail lights, and my battery is self contained.

I mounted it to my seat post but it sits off the side of the post instead of directly behind it like true tail lights. I did e-mail Cygolite about the experiment I did and made a few suggestions to improve the idea besides a new mount, and they actually responded back claiming they were going to send the info I gave them to R&D and have them look at it...right, probably them being polite when in reality what they meant to say was to get lost!! But here's a chance for a company to make a real bright tail light for about the same cost as Light and Motion vis 180 and be at least 3 times brighter. That has always been something I could never understand how a company can make a really bright 350 to 400 lumen head light for $100 but then come out with a wimpy 60 lumen tail light and charge $100...that's just weird in my little pea brain.

a lowrider BMX, a mountain bike, a faired recumbent, and a loaded touring bike

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I have TWO on this bike. They each have 13 LED's . Bought them at a NAPA Auto Parts Store. "Signal Stat" is the name of the manufacturer, as stamped into the plastic, but the bag they came in only said 'NAPA".

a lowrider BMX, a mountain bike, a faired recumbent, and a loaded touring bike

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This is the photo I meant to post earlier. There are 12 volt LED's on either rear corner of the panniers with two LED's in each. The center tail light is 12 volt and has three LED's. The other lights are 2xAAA blinkies; one on the left pannier, and one on the helmet (did you catch that? the helmet is sitting inverted in the right pannier) a sixth 2xAA blinkie is mounted on the seat post, but either I forgot to turn it on, or it is blocked from view by the helmet.
other angle:

Finally made some progress on this little project. I bought the LED trailer light off Amazon ($11 and change) that runs off 9-16 volts to combine with a 4000 mAH battery I had laying around from my HID light that I don't use anymore. Finished the wiring two nights ago with a three-way marine toggle switch, one setting for low (regular running light), another setting for high (brake/turn light switch). Used it for the first time today... it's very, very noticeable from a distance even on "low" due to the width of the light source. The "distance" shots really don't do the light justice, it's much easier to see than in the shots.

I used to use an led taillight like that on my folding bike. It was made for 12v and my dynamo hub was rated 6v but in a 16” wheel that hub puts out way more voltage than that. The lights were bright! But I never got a good headlight/taillight balance and eventual gave up on that type of taillight.

....I abandoned that *system ( *trailer type 12v lights ) because I got tired of carrying a heavy battery with wires run all over my bike. I like the new crop of battery powered tail lights that are available now.

That said: The light was dependable and bright. But it was bulky and inefficient compared to the nicer bicycle specific lights on the market.

Yes, I agree completely. Some of the new trailer type led lights do look bright but they do carry the extra baggage of being big and requiring a heavier/bigger battery. Their only redeeming feature is that they are cheap.

I think if size and weight were not an issue I'd get one of the Dinotte 400R light heads and just adapt the plug to a magicshine type battery ( which I already own ). Yes it would cost more than a home brew 12v system but in the end it wouldn't be that much more money ( if you already own a cache of 7.4v batteries ). Not to mention you would also get a brighter and more functional rear lamp.

Bottom line for most people though is going to be "simplicity". The new breed of mini self-contained rear lights are bright, functional, affordable and easy to mount. If you own a number of them they undoubtedly are going to get you seen.

My brightest tail light is a Cygolite ExpiliOn 450 that I converted from a head light to a tail light by putting 3 layers of red tail light tape used to fix broken tail lights. This gave me probably the brightest tail light available on the market with 450 lumens and I did it far cheaper then some other brands boasting 400 lumen tail lights, and my battery is self contained.

hi, I was really curious to see the result of converting ExpiliOn into a tail light, do you have any video of it showing the powerful result and willing to share please?

hi, I was really curious to see the result of converting ExpiliOn into a tail light, do you have any video of it showing the powerful result and willing to share please?

Unfortunately I can't seem to get pics downloaded off a camera into the computer then onto a forum, I can get them from the camera to the computer but for some reason everything I tried won't get it from the computer to a forum

I can tell you this, it's not a true red, more like a violet, not sure if that's because the quality of the tail light lens repair tape or because it is just that way. I tried one layer of tape and could hardly tell I put tape on it, put a second layer on it and it was a bright sort of washed out violet, but a third layer on it and it became a bright violet so I left it at that point. I can also tell you this, when compared to my old BlackBurn Mars 4 the converted ExpiliOn will cast a violet beam onto the wall in my basement, the Blackburn could do that too but it was obviously red but it wasn't as bright of a spot, and the ExpiliOn was a much larger diameter spot.

I tried that because the Blackburn battery case after many openings and closings the plastic got too chewed up to open anymore easily. BUT, there is one, possibly two faults with the ExpiliOn conversion...it has no side lighting, and I'm not sure if it's legal since it's not a true red. So in light of those one or two faults I'm looking into getting either a Serfas Shield or a Light and Motion Vis 180 (not the micro), or the odd one out is the Phillips Lumiring, but I can't find any comparison between European tail lights and the ones used in the US so the Phillips may be out of the equation.

Another odd one is the Reallite, but this thing is large at 4" x 6", but here's a video of it: http://www.youtube.com/watch?v=1qywt06pg4E I've seen a cyclist with one of these once and that thing was very impressive and easy to see from a long ways away.